Narcissists are very good at persuasion techniques and ways to get you to trust them, in order to lure you in.

If you felt right away that they were not to be trusted then you would not have continued onto the next level of intimacy with them.

Some narcissists actively study and train to learn these techniques and others just naturally develop them. Since they do not have to learn to follow the moral and ethical practices that other people do, it leaves them more time for learning these techniques by trial and error.

Narcissists want to control people in order to extract narcissistic supply or to use them as sources for narcissistic supply in some way.

They can control you better if they learn about you. In order to learn about you they need you to reveal things about yourself to them.